There is a projected global shortage for benzene which is needed in the manufacture of key petrochemicals such as styrene, phenol, nylon and polyurethanes, among others. Generally, benzene and other aromatic hydrocarbons are obtained by separating a feedstock fraction which is rich in aromatic compounds, such as reformates produced through a catalytic reforming process and pyrolysis gasolines produced through a naphtha cracking process, from non-aromatic hydrocarbons using a solvent extraction process.
In an effort to meet growing world demand for key petrochemicals, various industrial and academic researchers have been working for several decades to develop catalysts and processes to make light aromatics, benzene, toluene, xylenes (BTX) from cost-advantaged, light paraffin (C1-C4) feeds. Catalysts devised for this application usually contain a crystalline aluminosilicate (zeolitic) material such as ZSM-5 and one or more metals such as Pt, Ga, Zn, Mo, etc. to provide a dehydrogenation function. Aromatization of ethane and other lower alkanes is thermodynamically favored at high temperature and low pressure without addition of hydrogen to the feed. Unfortunately, these process conditions are also favorable for rapid catalyst deactivation due to formation of undesirable surface coke deposits which block access to the active sites of the catalyst.
One approach to circumvent this rapid deactivation problem is to devise a lower alkane aromatization process featuring one or more catalyst beds in which the catalyst bed(s) are cycled rapidly and continuously between reaction conditions suitable for aromatization to take place and regeneration conditions suitable for removing the accumulated coke from the catalyst to restore activity.
Due to the highly endothermic nature of the alkane aromatization reaction, there is a need to maintain a heat balance between the reaction and regeneration steps of the cycle.